The "Mortal Instruments" is a series of young adult fantasy novels written by Cassandra Clare. The story follows Clary Fray, a teenage girl who discovers she is part of a hidden world of Shadowhunters, human-angel hybrids tasked with protecting humanity from demons and other supernatural beings. The series explores themes of love, friendship, and identity as Clary navigates her new reality. Set in a richly detailed universe, the series includes various supernatural creatures such as werewolves, vampires, and fairies. The first book, "City of Bones," introduces readers to Clary's journey and her connection to the mysterious Jace Wayland, a skilled Shadowhunter. The series has gained a large following and has been adapted into a film and a television series.